I bought a spinet built in 1948 on Friday and I need two more thumbscrews to hold the main body onto the trestle stand. The thread on the one thumbscrew I've got is quite unusual, being a twin start type. The edges are rounded indicating that it might be a Whitworth but I can't find any reference on the web to twin start Whitworth threads.

 

The measurements are: diameter over thread peaks 6.3mm (1/4"), and just under 14TPI (that's just under 7TPI per thread).

 

Any ideas?

 

Thanks in advance!

 

 

No idea,

but i would maybe ask in a Musical Instrument shop / Piano Tuners.  

 

Or any Musical Instrument type forum might be of a help.

Edited 22 December, 201411 yr by goneoffSKi

Musical instrument makers often 'do their own thing' and it could be that your spinet comes under that heading, with everything hand-made. 

 

In your position, I'd be inclined to send lots of details and pics of the screw and the spinet in general to the Horniman Museum in London for comment.  The instrument itself might have a recorded history and the experts might have info about that rather unusual thread.  If that fails, you might have a look on line for a specialist machinist who could make duplicates. 

 

Good luck! 

Find a local instrument restorer and show them, but it will probably be a "unique" thread.

Won't be a two start whitworth as there isn't such thing. It would be easy enough for a local machine shop to make one up for you.

Hi. Looks like an "Acme" thread to me.

Certainly looks like a special.

Has a canny resemblance to a sash window bolt.  Maybe a reclamation yard.

 

I think a visit to friend with a lathe is in your future.

If you take the screw into an engineering works (like somewhere who do engine rebuilds or suchlike) they might have a thread gauge which will tell you what it is. My local machine shop sorted a strange bolt out for me a few years back.